I. Field of the Invention
The present invention relates generally to the field of reciprocating pumps. More particularly, the present invention relates to an improved reciprocating plunger pump boasting a self-aligning plunger assembly, a selectively removable plunger guide cartridge, and an improved seal cartridge assembly.
II. Discussion of the Prior Art
Plunger pumps may be characterized generally as including a plunger which reciprocates past a plurality of stationary seals so as to generate a pressurized fluid flow. FIG. 13 illustrates a plunger pump 10 typical of those employed in the prior art. The pump 10 includes a crankcase 12, a head assembly 14, and a reciprocating plunger assembly 16. The crankcase 12 includes an oil chamber 18, a plunger guide 20 for slidably receiving a plunger rod 22, and a drainage area 24 open to ambient. The head assembly 14 is two-piece in construction, including a first head member 26 and a second head member 28. Extending between the first head member 26 and the second head member 28 is a retainer 30 for forcibly maintaining a seal spreader 32 and a high pressure seal 34 within the second head member 28. The second head member 28 further includes a retaining slot for fixedly retaining a low pressure seal 36 therewithin. The plunger assembly 16 includes a reciprocating plunger 38 coupled to the plunger rod 22 via a retaining nut 40, and a connecting rod 44 extending between a rotatable crankshaft 42 and the plunger rod 22.
In order to prevent the migration of oil from the crankcase 12, a cartridge 46 is provided extending between the second head member 28 and the oil chamber 18 having an oil seal 48 for forming an oil-tight junction about the plunger guide 20 and a wiper member 50 for augmenting the sealing capability of the oil seal 48. In the event that oil does seep past the wiper member 50 and the oil seal 48, a plurality of weep holes 52 are formed in the cartridge 46 to allow any oil to drain out of the pump 10 by exiting through the drainage area 24. In order to prevent the unwanted migration of fluid from the head assembly 14, the seal spreader 32 is employed in conjunction with the high pressure seal 34 to form a fluid-tight junction with the plunger 38 which is capable of maintaining high fluid pressure within the head assembly 14. The low pressure seal 36 is also provided within the second head member 28 to maintain a low pressure fluid bath against the plunger 38 for the purpose of cooling the high pressure seal 34.
While generally effective, the pump 10 is nonetheless fraught with several formidable drawbacks. One of the more pronounced disadvantages relates to the construction of the plunger assembly 16. As is common in the prior art, the plunger rod 22 is coupled to the connecting rod 44 in a "press fit" fashion such that the plunger rod 22 is only capable of translating back and forth in a single plane. This "single plane" translation is problematic, however, in that the plunger rod 22 may be subject to side loading during operation due to any slight misalignment which may exist between the bores within the crankcase 12 and the head assembly 14. Such misalignment is not uncommon due, in part, to the multiplicity of components in the head assembly 14 which must be specifically co-aligned with the plunger guide 20 during the assembly process. The problem of side loading is particularly menacing in that it increases the degree of friction experienced by the seals within the head assembly 14 and crankcase 12, as well as the plunger rod 22 and plunger 38, due to the transverse forces exerted by the plunger rod 22 and plunger 38 during reciprocation. The increased friction elevates the temperature within the pump 10 which, in turn, disadvantageously causes the various seals to deteriorate prematurely and causes the plunger rod 22, the plunger 38, and the plunger guide 20 to experience accelerated wear and tear. From this stems increased costs for repair and/or replacement of the damaged components.
Another significant disadvantage stems from the fact that the plunger guide 20 is formed as a continguous portion of the crankcase 12. This is problematic in that the plunger guide 20 necessarily experiences abrasion due to the reciprocating action of the plunger rod 22 during pump operation. Over time, this abrasive activity will cause "scoring" wherein unwanted pits or grooves are formed in the plunger guide 20 and/or the plunger rod 22. The problem of "scoring" may manifest itself by causing oil to leak from the crankcase 12, as well as an overall reduction in pumping efficiency. To remedy this, the crankcase 12 must be replaced altogether. As will be appreciated, this requires a substantial amount of service time to dismantle all of the component parts from the crankcase 12 and reassemble them with a new crankcase 12. Crankcase replacement is also costly in that, as a relatively large part, the crankcase 12 consumes a large amount of material. Moreover, the plunger guide 20 must be specifically formed within the crankcase 12 and be machined in precise fashion to accept the plunger rod 22, thereby increasing the overall cost of manufacture. The plunger guide 20 also extends well into the interior of the crankcase 12 which, as will be appreciated, mandates that the plunger rod 22 is also of increased length to couple the connecting rod 44 to the plunger 38. Increasing the length of the plunger rod 22 excaserbates the problem of side loading which, as noted above, causes excess friction, high temperatures, seal deterioration, and "scoring" on the plunger rod 22 and the plunger guide 20.
Still other drawbacks with the prior art pump 10 relate to the seal arrangement. First and foremost, the pump 10 fails to provide the various seals in a readily accessible and conveniently removable fashion such that servicing operations, such as seal repair and/or replacement, are laborious and time consuming. For example, the low pressure seal 36 is disposed completely within the confines of the second head member 28, the seal spreader 32 and the high pressure seal 34 are force fit in between the retainer 30 and the second head member 28, and the oil seal 48 is disposed within the far end of the cartridge 46. In this arrangement, a serviceperson must thus remove the first head member 26, the retainer 30, the second head member 28, and the cartridge 46 to avail all of the sealing members for maintenance or replacement. This is particularly disadvantageous in that it is burdensome and time consuming to dismantle this host of pump parts every time the seals require servicing. The task of servicing is furthermore made difficult due to the fact that the low pressure seal 36 is effectively buried within the second head member 28 which, as will be appreciated, requires substantial effort to remove and replace the low pressure seal 36.
Another related drawback is that the sealing arrangement permits air to migrate from the drainage area 24 into the head assembly 14 during priming operations and negative pressure conditions at the fluid inlet 54. This stems from the fact that the low pressure seal 36 is incapable of forming an adequate seal about the plunger 38 during such conditions. To further explain, the low pressure seal 36 is a standard U-cup which forms a uni-directional seal along the plunger when properly energized or expanded. The necessary energization occurs when low pressure fluid is allowed to flow between the low pressure seal 36 and the high pressure seal 34 such that the U-cup expands inwardly and envelops the plunger 38 to form a seal therealong. While the low pressure seal 36 is effective in minimizing the degree to which low pressure fluid may seep into the drainage area 24 when properly energized, air will nonetheless flow inwardly past the low pressure seal 36 during priming operations due to the fact that there is little or no fluid pressure to adequately bias the low pressure seal 36 against the plunger 38. This increases the likelihood of producing an air-lock condition within the head assembly 14 which may inhibit or altogether thwart priming operations within the pump 10. Negative pressure conditions at the fluid inlet 54 may occur, for example, when the fluid reservoir supplying coupled to the fluid inlet 54 is disposed below the pump 10. Such negative pressure also acts upon the low pressure seal 36 in that the fluid inlet 54 is coupled to the channel defined between the high and low pressure seals 34, 36. Negative pressure at the low pressure seal 36, in turn, causes the low pressure seal 36 to lose its charge such that air may be drawn therepast into the fluid inlet 54 and ultimately into the head assembly 14. During operation, such an influx of air into the fluid inlet 54 may cause cavitation which, as will be appreciated, adversely affects the efficiency and life expectancy of the pump 10.
In view of the foregoing, a need exists for an improved plunger pump which overcomes the aforementioned deficiencies in the prior art.